1. Field of the Invention
This invention relates to the formation of a composite article by use of a rigid female mold, in combination with a flexible male mold, and will be hereinafter referred to as the Rigid/Flexible Mold System, or simply as "RFMS" technology. The flexible male mold includes a flexible wall placeable an adjustable distance away from the reference surface of the rigid female mold, with the composite article being formed therebetween.
2. Discussion of the Prior Art
Referring now to FIG. 1 in the prior art practice of resin transfer molding, a continuous strand mat 100 or a preformed reinforcement is positioned into an open mold. A rigid cooperatively shaped male mold 102 is mated to the first (female) mold 104 and clamped together. A catalyzed resin 106 mix is thereafter pumped into the cavity formed between the two molds. After a suitable curing cycle, the part is removed from the molds. Foam encapsulation, inserts, and the inclusion of a gel coat on the finish surface are available options during the practice of this process. Resin transfer molding is noted for the use of low pressure injection of the resin system (50 to 70 psi) and the use of directed fiber preforms.
(For the sake of clarity it should be noted, at this point in the specification, that the present RFMS technology offers a still lower resin injection pressure (10 to 30 psi), and preforming of the fibers directly onto the male mold. The technique of forming the fibers directly on the male mold is possible because the male mold is light enough to be easily turned over. Furthermore, the use of a unique instant set binder makes it possible for the glass fiber to hold to the male mold without the use of suction air flow to hold it to the mold until the binder cures.)
Referring now to FIG. 2 in the process of cold press molding fiber reinforcement 108 (preform or mat) is supplied between matching molds, 112, 114 along with thermosetting resin 110. Woven roving may be added for strength. The molds may be previously gel coated. The resin system is applied before the molds are closed under moderate pressure (20 to 50 psi), and the part is cured without heat other than the exothermic heat generated. Elevated molding pressures are not necessary.
(The RFMS technology borrows from the cold press molding process in that the resin system is successfully applied after the preform has been placed in the mold, but the resin is applied after the mold set is closed, so as to reduce toxic emissions. It is possible to apply the resin after the molds are closed by having the male mold divert away from the incoming resin stream, the male mold being flexible. Once the resin is in the mold cavity, the male mold is forced to its proper shape by internal vacuum and by external air pressure and/or steam.)
Referring now to FIG. 3, in the process of vacuum bag molding a flexible film 116 (PVA or cellophane) is placed over the completed wet layup 118 or sprayup, its joints are sealed, and a vacuum is thereafter drawn by vacuum pump 120. The atmospheric pressure (hopefully) eliminates voids in the laminate and forces excess resin and air from the mold.
(The RFMS technology also uses an internal vacuum drawn on the laminate so as to force excess resin and air from the mold. The RFMS technology, however, takes this concept two steps further. First, a semi-rigid male mold is used instead of the dimensionally pliant PVA or cellophane. The semi-rigid male mold "stamps" accurate and repeatable wall thickness into the finished article. Second, in the RFMS process, a fiberglass preform is used and the resin is injected into the perform while the preform is in the mold cavity. This replaces the tedious hand layup or sprayup process in vacuum bag molding with a clean "one shot" process).
Referring now to FIG. 4, the prior art pressure bag molding process utilizes a tailored rubber sheet 122 which is placed against the finished layup or sprayup 122, and air pressure is thereafter applied by blower 124 between the rubber sheet and the pressure plate 126. The pressure eliminates voids and drives excess resin and air out of the laminate so as to densify it and to improve the off-mold surface finish. This process is not compatible with male molds.
(The RFMS technology also utilizes a pressure plate on the male mold to force the excess air and resin out, but improves on this idea by utilizing a semi-rigid male mold that will "stand alone" as the shape of the part to be molded. In pressure bag molding, the tailored rubber sheet is the shape of the part only if it is inside the female mold and under pressure, similar to the film and vacuum bag molding.)
Referring now to U.S. Pat. No. 2,744,043, entitled "Method of Producing Pressure Containers for Fluids", fiberglass threads or threads of other suitable material are applied "wet", (resin saturated), in a mutually super imposed relationship on a removable inflatable core member, in a method generally known as the filament winding process, to manufacture pressure containers. The core member comprises an inflatable mandrel positioned within the windings which may be deflated for removal. The cylindrical shape of the inflatable bladder however, does not allow for any integrally co-cured beam-shaped stiffening inserts to be included about the interior surface of the structure to be molded.
The method disclosed in U.S. Pat. No. 4,126,659 also has similar limitations in that internal stiffeners can not be incorporated in the composite structure during one molding operation, but must be added on in another process step, if desired.
A method and apparatus therefore need to be developed that will incorporate the aforementioned advantages over the resin transfer molding, cold press molding, vacuum bag molding, and pressure bag molding processes, as well as allow the lamination of internal stiffeners within the final composite article in a one step process.